期刊
ASTROPHYSICAL JOURNAL
卷 744, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/744/2/93
关键词
galaxies: abundances; galaxies: ISM; quasars: absorption lines
资金
- NASA [NAS 5-26555, HST-GO-11598.03-A, NNX08AJ44G]
- NSF [AST-0709235]
- W.M. Keck Foundation
- NASA [NNX08AJ44G, 100420] Funding Source: Federal RePORTER
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1109447] Funding Source: National Science Foundation
We present Cosmic Origins Spectrograph (COS) measurements of metal abundances in eight 0.083 < z(abs) < 0.321 damped Ly alpha (DLA) and sub-DLA absorption systems serendipitously discovered in the COS-Halos survey. We find that these systems show a large range in metallicities, with -1.10 < [Z/H] < 0.31, similar to the spread found at higher redshifts. These low-redshift systems on average have subsolar metallicities, but do show a rise in metallicity over cosmic time when compared to higher-redshift systems. We find that the average sub-DLA metallicity is higher than the average DLA metallicity at all redshifts. Nitrogen is underabundant with respect to alpha-group elements in all but perhaps one of the absorbers. In some cases, [N/alpha] is significantly below the lowest nitrogen measurements in nearby galaxies. Systems for which depletion patterns can be studied show little, if any, depletion, which is characteristic of Milky Way halo-type gas. We also identify affiliated galaxies for three of the sub-DLAs using spectra obtained from a Keck/Low Resolution Imaging Spectrometer (LRIS). None of these sub-DLAs arise in the stellar disks of luminous galaxies; instead, these absorbers may exist in galaxy halos at impact parameters ranging from 38 to 92 kpc. Multiple galaxies are present near two of the sub-DLAs, and galaxy interactions may play a role in the dispersal of the gas. Many of these low-redshift absorbers exhibit simple kinematics, but one sub-DLA has a complicated mix of at least 13 components spread over 150 km s(-1). We find three galaxies near this sub-DLA, which also suggests that galaxy interactions roil the gas. This study reinforces the view that DLAs have a variety of origins, and low-redshift studies are crucial for understanding absorber-galaxy connections.
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